Paperboard boxes having attached lids and constructed from a single blank of material are known. Such a container is shown in U.S. Pat. No. 2,210,443. Such containers are useful for protecting many items, including "fast food" sandwiches. The container shown in the referenced patent includes a pair of front corner constructions that are commonly known as "Beers" corners and can be erected from a flat collapsed position to an erected position. However, the normal Beers corner construction includes no locking structure to prevent inadvertent re-collapse of the container during or after loading of the contents. Also, the normal Beers corner tends to sag because of the springiness of the paperboard, so that the container is not held fully open for loading of the contents.
Attempts have been made to lock erectable containers in erected form. For example, in U.S. Pat. No. 1,838,191, inner side walls are folded upwardly against outer side walls to form a double thick side wall. The inner side walls include tabs that catch on ribs extending from the intersecting end walls to hold the inner side walls in position. In U.S. Pat. No. 2,650,751, the side walls themselves are formed to raise upwardly and outwardly as the carton is erected. A special double flap along the front wall of the container catches and traps the side walls in their erected position, and protuberances extending into the container from the back wall tend to trap the rear vertical edge of the side walls.
Locking mechanisms have also been provided in connection with Beers corners. In the typical Beers corner construction, perpendicular wall panels are foldably connected to a bottom panel, and a glue flap is foldably connected to one of the wall panels and adhered to the interior surface of the other wall panel near the top edge of the wall panel. A diagonal score or perforation in the wall panel separates the area adhered to the glue panel from the area below the score or perforation. Prior trays have been provided in which a drag tab extends from the bottom of the glue panel to frictionally engage the bottom panel of the container as the Beers corner is erected. A tab of material is broken out of the bottom panel where it intersects the wall panel beneath the drag tab to leave a cut out opening for receiving the drag tab. Both the tab of material broken out of the bottom panel and the drag tab extend through the cut out opening below the bottom of the box, creating a sometimes undesirable projection which prevents the container from resting flat on its bottom surface. Additional cutouts are provided in the wall panel to which the glue panel is foldably connected in order to accommodate the drag tab when the container is collapsed, since the drag tab would otherwise be jammed in the score between the wall panel and the bottom panel. In such prior art trays, the cutouts for receiving the drag tab when the carton is erected have been placed immediately adjacent to the wall panel, so that it is necessary to force the drag tab completely into the corner between the wall panel and bottom panel in order to insert it into the cutout and thereby lock the corner.
Thus, there has been a need for a locking mechanism associated with Beers corners which can be easily activated and which does not result in the projection of tabs through the bottom of the container.